Councillors will be asked to sign a disclaimer when they study new figures backing the case for a scaled-back line.

After a lengthy debate in the city chambers yesterday, councillors voted to demand details of the new business case for halting the line at St Andrew Square. They also asked for the report to include a cost scale for the first phase, projected passenger numbers and what impact it might have on Lothian Buses.

They will be under strict instruction not to reveal any commercial details. The agreement came after the SNP's third failed effort to halt the tram project. Main contractor Bilfinger Berger is still locked in legal talks with TIE over how much work can be done with existing funds.

On their way in to the meeting some councillors took leaflets from bus drivers who held a protest outside. They too were calling on more clarity, fearing the long-standing proposal to merge Lothian Buses with Transport Initiatives Edinburgh (TIE) to create Transport Edinburgh Limited (TEL) could be damaging.

Today Lothian Buses chairman David Mackay and chief executive Ian Craig had what they said was a constructive meeting with Unite union representatives. They reiterated that, as plans currently stand, TEL will not change the existing Lothian Buses fares policy, service levels or staff terms and conditions.

Mackay said after the meeting:

"Lothian Buses is a much cherished part of life in Edinburgh and the Lothians. The board and I are personally extremely proud of the track record and heritage which the company has. We (and this includes the leaders of the council) hold very dear the name and reputation and success of the business.

"I would like to reiterate again, loudly and clearly that there is no threat to this proud name in the formation of TEL. Lothian Buses will remain as a discrete name and brand and Edinburgh Trams will learn from your many skills and unrivalled experience."

Green councillor Steve Burgess said he voted to look at the new business case plans so he could check whether the drivers' concerns were valid and to be certain the figures stacked up.

He said:

"Lothian Buses sent us an email saying they were concerned their position would be compromised if their figures fell into the hands of competitors. I agree that information should remain private but we need to be sure the business case is sound.

"We are being told it is sound, but I am glad some elected members will get the opportunity to check."

Labour leader Andrew Burns said signing a disclaimer was 'insulting' and hit out at the SNP for trying to halt the scheme.

He said:

"I'm disappointed with the way the meeting turned out. The amendment we put forward was based on what people were telling us. They told us the key was a lack of detail in the business case for TEL.

"We will get the full detail, but it won't be in the public domain. Of course if I was asked to sign a disclaimer I would respect that but I find it insulting.

"Halting the project would be irresponsible and anti-Edinburgh. Nearly £400m has been spent and it seems incredibly naive to not do anything with that."

Lothians MSP Shirley-Anne Somerville of the SNP said she supported her council colleagues' bid to halt the project. She also said she was against using Lothian Buses to subsidise the tram funding problems.

Somerville said:

"Even people who were originally tram supporters are so frustrated with the mishandling of this project that they too now want to see an end to this waste of public money. Instead of a 'network' all we're being offered is a subsidised half tram line – so I have no idea why Labour, Lib Dems, Tories and Greens still seem determined to carry on regardless.

"TIE have lost all credibility. They are unable to tell us when and at what cost the half tram line will be finished – and even if they provided figures there is no reason why we should find them any more credible than their earlier estimates.

"TIE's idea that the half tram line should be subsidised by Lothian Buses for three years is a very worrying development. They're already doing damage to Edinburgh businesses – I don't want to see them damaging the excellent bus network as well".

Although the merger plans are not new, the drivers took a stance yesterday as councillors were discussing the possible creation of Transport Edinburgh Limited.

It is proposed this body would be made up of tram firm TIE and Lothian Buses, whose drivers held placards outside the city chambers.